A conventional gas turbine engine includes in serial flow communication a compressor, a discharge flowpath having compressor outlet guide vanes (OGVs) and a combustor diffuser, a combustor, a turbine nozzle, and a high pressure turbine. During engine operation, the compressor compresses inlet airflow, which is therefore heated thereby, with the discharged compressed and heated airflow being channeled through the OGVs and the diffuser to the combustor wherein it is conventionally mixed with fuel and ignited to form combustion gases. The combustion gases are channeled through the turbine nozzle to the high pressure turbine which extracts energy therefrom for rotating and powering the compressor.
In one typical embodiment, the OGVs and the combustor diffuser include an annular inner support extending downstream to the turbine nozzle which supports the turbine nozzle. An annular outer support extends radially outwardly from the OGVs and the diffuser and is fixedly connected to the casing surrounding the engine for supporting the OGVs and the diffuser, which, in turn, supports the turbine nozzle.
The turbine nozzle includes a plurality of circumferentially spaced and angled nozzle vanes which conventionally direct the combustion gases into the high pressure turbine. A pressure drop exists across the turbine nozzle and the inner support which generates an axial force which is carried upstream through the inner support, the discharge flowpath, and the outer support to the casing. Since the nozzle vanes are angled, a circumferential component of force is also generated from the combustion gases which results in a torque relative to the engine centerline axis also being transmitted upstream through the inner support and the outer support to the casing.
During an engine thermal transient such as, for example, throttle push, the compressor OGVs and combustor diffuser experience relatively high and nearly instantaneous temperature change due to the relatively hot compressed airflow being discharged from the compressor. Although the inner support responds relatively quickly with the OGVs and the diffuser, the outer support and casing respond relatively slowly to the temperature change. Therefore, the OGVs and diffuser expand more rapidly relative to the outer support which outer support tends to restrain the radial growth thereof resulting in relatively high thermally induced stress at the interface thereof.
The outer support is typically an annular, conical or cylindrical, surface of revolution or shell, which is relatively stiff requiring relatively large forces to cause deflection thereof. The relatively large thermal mass of the OGVs and combustor diffuser create both a radially outward deflection and rotation of the end of the relatively slowly expanding outer support connected thereto, with attendant large thermal stresses therein. In other words, the supporting end of the outer support shell is caused by the expanding OGVs and diffuser to both expand and twist radially outwardly relative to the outer support shell at distances away from its interface with the OGVs and the diffuser.
Accordingly, the relatively quickly expanding OGVs and diffuser expand radially outwardly to a greater extent than the relatively slowly expanding outer support shell resulting in a differential thermal movement, or expansion, therebetween. This differential thermal movement is accommodated by the bending of the outer support shell at its intersection with the OGVs and diffuser resulting in high thermal stress therein.